Present-day internal combustion engines according to the principle of the gasoline engine are operated as a rule with a fuel extracted from crude oil and containing hydrocarbons such as regular or premium gasoline. Alternatively alcohol fuels extracted from plants, for example from sugar cane, such as ethanol are also increasingly being used.
A motor vehicle, which takes both kinds of fuel, is referred to as a vehicle capable of adapting to the fuel, or also as a “flexible fuel vehicle”, or in short as a “flex-fuel vehicle” (FFV) or as a flex-power vehicle. These types of vehicles can be operated with pure gasoline as well as with various similar fuels like, for example, ethanol, bioethanol or methanol-gas mixtures. Pure ethanol is denoted as E100-fuel. Pure gasoline is on the other hand denoted as E0-fuel. Any arbitrary mixture with xx % ethanol is denoted as Exx. In Europe, Brazil and the USA, typical fuels containing ethanol comprise approximately 75 to 85% ethanol (E75, respectively E85). The remaining 15 to 25% is gasoline.
Because ethanol has a significantly smaller stoichiometric ratio during combustion when compared with gasoline (9.0 instead of 14.7), an increased injected fuel quantity is required in a stoichiometric engine operation with ethanol. This is made more complicated by the fact that arbitrary mixtures can occur in the fuel tank as a result of the fuels put in the tank. Information about a past fueling of the tank must at the latest be present when after filling the tank, new fuel with other characteristics has arrived at the fuel distributor rail, the so-called fuel rail, respectively at the fuel-delivery control system of the internal combustion engine. An exact knowledge of the ethanol content of the fuel significantly improves the drivability of the vehicle as well as the cold starting capability and the degree of efficiency achieved by the adjustment of the parameters of the engine management system.
The engine management system of the flex-fuel vehicle must therefore adjust the engine mode of operation, especially the fuel injection mode of operation, respectively the fuel injection characteristic diagrams and the ignition characteristic diagrams, to the corresponding fuel-mixture ratio. Detection with certainty of the fuel-mixture ratio existing in the tank is required for this purpose. In so doing, it is assumed that the mixture ratio can only then change in the tank if a quantity of fuel has been added. For this reason a leading role is assigned to the fueling detection in a flex-fuel system.
State of the art is a detection, which detects the fuel level change in a vehicle at rest (fuel tank sender, signal at terminal 15). Fueling when the motor is running is not detected. The disadvantage thereby is that the fuel level measured in a vehicle at rest depends very greatly on the degree to which the vehicle is slanted. An improved fueling detection is described in a parallel application of the applicant (female).
In current flex-fuel systems the isolation of map-based pilot control errors of the fuel-mixture control, which result, for example, from variances in the dispersions of the fuel injection valves or leakages in the intake manifold, and the use of fuel containing ethanol represent large challenges. As a result of insufficient discrimination, the possibility exists that the fuel-mixture errors are mistakenly subscribed to the proportion of ethanol in the fuel or the reverse is true.
It is therefore the task of the invention to provide a method, which allows changes in the ethanol content of the fuel to be distinguished from map-based pilot control errors during the fuel-mixture preparation.